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        <h3 id="this指向"><a href="#this指向" class="headerlink" title="this指向"></a>this指向</h3><ul>
<li><p>this指向：谁调用this就是指向谁，默认指向window  fn()等价于window.fn()</p>
</li>
<li><p>全局调用普通函数：严格模式下指向undefined；非严格模式下执行window</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">&lt;script&gt;</span><br><span class="line"><span class="meta">    &#x27;use strict&#x27;</span></span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(tihs)   <span class="comment">// undefined</span></span><br><span class="line">    &#125;</span><br><span class="line">    fn()</span><br><span class="line">&lt;/script&gt;</span><br><span class="line">&lt;script&gt;</span><br><span class="line">    functoin <span class="function"><span class="title">fn</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="built_in">this</span>)  <span class="comment">// window</span></span><br><span class="line">    &#125;</span><br><span class="line">    fn()</span><br><span class="line">&lt;/script&gt;</span><br></pre></td></tr></table></figure></li>
<li><p>定时器中this：定时器中的this默认指向window（除了特殊指向），因为定时器都是定义在window下面的</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">setTimeout</span>(<span class="function">()=&gt;</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="built_in">this</span>)   <span class="comment">// window</span></span><br><span class="line">    &#125;)</span><br><span class="line">&#125;</span><br><span class="line">fn();</span><br><span class="line"></span><br><span class="line"><span class="comment">// 修改定时器中this的指向</span></span><br><span class="line"><span class="keyword">const</span> obj = &#123;</span><br><span class="line">    name:<span class="string">&#x27;lisi&#x27;</span>,</span><br><span class="line">    fn:<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">setTimeout</span>(<span class="function">()=&gt;</span>&#123;</span><br><span class="line">            <span class="built_in">console</span>.log(<span class="built_in">this</span>);  <span class="comment">// this指向对象obj</span></span><br><span class="line">        &#125;,<span class="number">1000</span>)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></li>
<li><p>对象中this的指向</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">const</span> obj = &#123;</span><br><span class="line">    name:<span class="string">&#x27;lisi&#x27;</span>,</span><br><span class="line">    age:<span class="number">12</span>,</span><br><span class="line">    sex:<span class="string">&#x27;男&#x27;</span>,</span><br><span class="line">    fn:<span class="function"><span class="keyword">function</span> (<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="string">&quot;姓名：&quot;</span>,<span class="built_in">this</span>.name,<span class="string">&quot;--&quot;</span>,<span class="string">&quot;年龄&quot;</span>,<span class="built_in">this</span>.age,<span class="string">&quot;--&quot;</span>,<span class="string">&quot;性别&quot;</span>,<span class="built_in">this</span>.sex)  <span class="comment">// 对象调用了方法，this指向对象本身</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line">obj.fn();</span><br></pre></td></tr></table></figure></li>
<li><p>嵌套函数中this指向，非严格模式指向window，严格模式指向undefined</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">foo</span>(<span class="params">name</span>)</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="built_in">this</span>)</span><br><span class="line">    &#125;</span><br><span class="line">    foo(<span class="string">&#x27;lisi&#x27;</span>)  <span class="comment">// 等价于window.foo(&#x27;lisi&#x27;) 所以指向window</span></span><br><span class="line">&#125;</span><br><span class="line">fn()</span><br></pre></td></tr></table></figure></li>
<li><p>箭头函数没有this，箭头函数里面的this是其外围的this,定时器里面的箭头函数的this指向window</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">setTimeout</span>(<span class="function">()=&gt;</span>&#123;</span><br><span class="line">    <span class="keyword">const</span> fn = <span class="function">()=&gt;</span>&#123;</span><br><span class="line">        <span class="built_in">console</span>.log(<span class="built_in">this</span>)</span><br><span class="line">    &#125;</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure></li>
<li><p>构造函数的this:指向实例化对象</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">this</span>.name = <span class="string">&#x27;lisi&#x27;</span></span><br><span class="line">    <span class="built_in">console</span>.log(<span class="built_in">this</span>)</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">const</span> Fn = <span class="keyword">new</span> fn();</span><br></pre></td></tr></table></figure>

</li>
</ul>
<h3 id="改变this的指向：call-apply-bind"><a href="#改变this的指向：call-apply-bind" class="headerlink" title="改变this的指向：call()/apply()/bind()"></a>改变this的指向：call()/apply()/bind()</h3><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// call()</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">    name:<span class="string">&#x27;lisi&#x27;</span>,</span><br><span class="line">    age:<span class="number">13</span>,</span><br><span class="line">    sex:<span class="string">&#x27;男&#x27;</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">x,y</span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">&#x27;姓名：&#x27;</span>,<span class="built_in">this</span>.name,<span class="string">&#x27;-&#x27;</span>,<span class="string">&#x27;年龄&#x27;</span>,<span class="built_in">this</span>.age,<span class="string">&#x27;性别&#x27;</span>,<span class="built_in">this</span>.sex,x,y)</span><br><span class="line">&#125;</span><br><span class="line">fn.call(obj,<span class="string">&#x27;1&#x27;</span>,<span class="string">&#x27;2&#x27;</span>)  <span class="comment">// 普通函数默认指向window，通过call()改变this的指向，指向obj对象</span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">//apply</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">    name:<span class="string">&#x27;lisi&#x27;</span>,</span><br><span class="line">    age:<span class="number">13</span>,</span><br><span class="line">    sex:<span class="string">&#x27;男&#x27;</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">x,y</span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">&#x27;姓名：&#x27;</span>,<span class="built_in">this</span>.name,<span class="string">&#x27;-&#x27;</span>,<span class="string">&#x27;年龄&#x27;</span>,<span class="built_in">this</span>.age,<span class="string">&#x27;性别&#x27;</span>,<span class="built_in">this</span>.sex,x,y)</span><br><span class="line">&#125;</span><br><span class="line">fn.apply(obj,[<span class="number">1</span>,<span class="number">2</span>])  <span class="comment">// apply()与call()方法不同的是，apply只接受两个参数，一个是this,另一个是参数数组</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//bind()</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">    name:<span class="string">&#x27;lisi&#x27;</span>,</span><br><span class="line">    age:<span class="number">13</span>,</span><br><span class="line">    sex:<span class="string">&#x27;男&#x27;</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">x,y</span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="string">&#x27;姓名：&#x27;</span>,<span class="built_in">this</span>.name,<span class="string">&#x27;-&#x27;</span>,<span class="string">&#x27;年龄&#x27;</span>,<span class="built_in">this</span>.age,<span class="string">&#x27;性别&#x27;</span>,<span class="built_in">this</span>.sex,x,y)</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">const</span> a = fn.bind(obj)  <span class="comment">// 改变this指向，bind()创建的是一个新的函数，当目标函数被调用时，this的值绑定到bind()的第一个参数上</span></span><br><span class="line">a()</span><br></pre></td></tr></table></figure>

<ul>
<li>apply/call/bind三这之间的区别</li>
<li>相同点：都是改变this的指向；当第一个参数为undefined和null时，this默认指向window</li>
<li>不同点：传递参数的方式不同，call()传递的参数列表，apply传递的是参数数组，bind传递的是参数列表，但是bind返回的是函数，需要重新调用</li>
</ul>
<h3 id="浅拷贝和深拷贝"><a href="#浅拷贝和深拷贝" class="headerlink" title="浅拷贝和深拷贝"></a>浅拷贝和深拷贝</h3><ul>
<li>浅拷贝只会复制指向某个对象的指针，而不是对象本身，新旧对象还是在共享同一内存，修改新对象，旧对象也会跟着修改<ul>
<li>实现方式：<ul>
<li>通过等号直接复制</li>
<li>Object.assign()方法可以把任意多个的源对象自身的可枚举属性拷贝给目标对象，然后返回目标对象。但是 Object.assign()进行的是浅拷贝，拷贝的是对象的属性的引用，而不是对象本身<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: &#123;<span class="attr">a</span>: <span class="string">&quot;kobe&quot;</span>, <span class="attr">b</span>: <span class="number">39</span>&#125; &#125;;</span><br><span class="line"><span class="keyword">var</span> initalObj = <span class="built_in">Object</span>.assign(&#123;&#125;, obj);</span><br><span class="line">initalObj.a.a = <span class="string">&quot;wade&quot;</span>;</span><br><span class="line"><span class="built_in">console</span>.log(obj.a.a); <span class="comment">//wade</span></span><br></pre></td></tr></table></figure>
但是当对象只有一层的时候，object.assign()是深拷贝<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj = &#123;<span class="attr">username</span>: <span class="string">&#x27;kobe&#x27;</span>&#125;;</span><br><span class="line"><span class="keyword">let</span> obj2 = <span class="built_in">Object</span>.assign(&#123;&#125;,obj);</span><br><span class="line">obj2.username = <span class="string">&#x27;wade&#x27;</span>;</span><br><span class="line"><span class="built_in">console</span>.log(obj);<span class="comment">//&#123;username: &quot;kobe&quot;&#125;</span></span><br></pre></td></tr></table></figure></li>
</ul>
</li>
<li>Array.prototype.concat() 和 Array.prototype.slice()</li>
<li></li>
</ul>
</li>
<li>深拷贝：创造出一个新的对象，新旧对象不共享内存，修改新对象不会改变旧对象的值<ul>
<li>实现方式：<ul>
<li>JSON.parse(JSON.stringify())：用JSON.stringify将对象转成JSON字符串，再用JSON.parse()把字符串解析成对象，一去一来，新的对象产生了，而且对象会开辟新的栈，实现深拷贝</li>
<li>使用Object.create()方法：var newObj = Object.create(oldObj)</li>
<li>第三方函数：lodash</li>
</ul>
</li>
</ul>
</li>
</ul>

      
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